This invention relates to a process for reducing poisonous effects of metal contaminants picked up by a hydrocarbon conversion catalyst during a hydrocarbon conversion process such as the high temperature conversion of a hydrocarbon feedstock containing such metals to a lower boiling product. More particularly, this invention relates to processes for reducing the poisonous effects of metal contaminants without removal of such contaminants from the catalyst, e.g., by a process of passivation.
During a catalyst promoted chemical conversion of a hydrocarbon containing metal contaminants such as iron, nickel and vanadium, the catalyst becomes more and more deactivated due to the pick up of at least a portion of the metal contaminants. Removal of such poisons from the catalyst may restore a substantial amount of the catalytic activity. However, no matter how carefully the process for the removing the metal poisons from the catalyst is carried out, some penalty in the form of overall performance is often paid. Accordingly, a simple and straight forward method of overcoming the deleterious effects of the metal poisons or contaminants is desirable.
Catalytically promoted methods for the chemical conversion of hydrocarbons include cracking, hydrocracking, reforming, hydrodenitrogenation, hydrodesulfurization, etc. Such reactions generally are performed at elevated temperatures, for example, about 300.degree. to 1200.degree. F., more often 600.degree. to 1000.degree. F. Feedstocks to these processes comprise normally liquid or solid hydrocarbons which, at the temperature of the conversion reaction, are generally in a fluid, i.e., liquid or vapor, state and the products of the conversion usually are more valuable, lower boiling materials.
Although referred to as "metals", these catalyst contaminants may be present in the hydrocarbon feed in the form of free metals or relatively non-volatile metal compounds. It is, therefore, to be understood that the term "metal" as used herein refers to either form. Various petroleum stocks have been known to contain at least traces of many metals. For example, Middle Eastern crudes contain relatively high amounts of several metal components, while Venezuelan crudes are noteworthy for their vanadium content and are relatively low in other contaminating metals such as nickel. In addition to metals naturally present in petroleum stocks, including some iron, petroleum stocks also have a tendency to pick up tramp iron from transportation, storage and processing equipment. Most of these metals, when present in a stock, deposit in a relatively non-volatile form on the catalyst during conversion processes so that regeneration of the catalyst to remove deposited coke does not also remove these contaminants. With the increased importance of gasoline in the world today and the shortages of crude oils and increased prices, it is becoming more and more important to process any type or portions of a crude source, including those highly metal contaminated crudes to more valuable products.
Of the various metals which are to be found in representative hydrocarbon feedstocks some, like the alkali metals, only deactivate the catalyst without changing the product distribution; therefore, they might be considered true poisons. Others such as iron, nickel, vanadium and copper markedly alter the selectivity and activity of cracking reactions if allowed to accumulate on the catalyst and, since they affect process performance, they are also referred to as "poisons". A poisoned catalyst with these metals generally produces a higher yield of coke and hydrogen at the expense of desired products, such as gasoline and butanes. For instance, U.S. Pat. No. 3,147,228 reports that it has been shown that the yield of butanes, butenes and gasoline, based on converting 60 volume percent of cracking feed to lighter materials and coke dropped from 58.5 to 49.6 volume percent when the amount of nickel on the catalyst increased from 55 ppm to 645 ppm and the amount of vanadium increased from 145 ppm to 1480 ppm in a fluid catalytic cracking of a feedstock containing some metal contaminated stocks. Since many cracking units are limited by coke burning or gas handling facilities, increased coke or gas yields require a reduction in conversion or throughput to stay within the unit capacity.
Several U.S. patents exemplifying the passivation approach to reducing the poisonous effects of metal contaminants on a conversion catalyst are discussed hereinafter.
U.S. Pat. No. 2,901,419 (1959) discloses a method for preventing undesirable catalytic effects during a catalytic conversion of a hydrocarbon feedstock than would otherwise result from an accumulation of metal or metal-containing impurities, e.g., iron, nickel and/or vanadium, on a catalyst surface. The method comprises introducing together with the contaminated catalyst is a catalyst zone, at least one material selected from the group consisting of metals of the periodic system of Groups III and IV, and metals of the right-hand subgroups of Groups I and II of the periodic system. Specific metals named from the cited groups were copper, silver, gold, tin, zinc, cadmium and mercury. The catalyst zone discussed in the examples was a muffle furnace at 1000.degree. F. for two hours. Powdered zinc and powdered zinc fluoride were the only materials used in the examples to demonstrate the invention.
U.S. Pat. No. 3,711,422 (1973) discloses a method for restoring the activity of metal contaminated cracking catalysts by a passivation process involving antimony containing compounds which are either oxides or convertible to oxides of antimony upon calcination. The passivation process involves contacting the cracking catalyst with antimony-containing compounds so as to deposit them on the catalyst, e.g., by impregnation, dry mixing or deposition from suitable carrying agents.
U.S. Pat. No. 4,031,002 (1977) discloses a method for passivating metal contaminants, e.g., nickel, vanadium and/or iron in a catalyst by contacting such a catalyst with an antimony compound containing phosphorodithioate ligands having the following general formula: ##STR1## wherein the R groups which can be the same or different are hydrocarbyl radicals containing from 1 to about 18 carbon atoms per radical, the total number of carbon atoms per antimony compound molecule being from 6 to about 90.
The disclosed phosphorus and antimony compounds can be added to the feedstock prior to the cracking zone. There is no suggestion that the phosphorus present in the antimony compound plays an active role in the metals passivation process. Only the concentration of the antimony present in these compounds in relation to the amount of metal contaminants either in the feed or on the contaminated catalyst are considered. The importance of the phosphorus beyond its usefulness in providing a stable organic soluble antimony compound is neither suggested nor disclosed.
U.S. Pat. Nos. 4,148,712 (1979) and 4,148,714 (1979) both disclose the use of cracking catalyst fines from a cracking process wherein antimony or a compound thereof had been used as a metals passivation agent for metals such as nickel, vanadium and/or iron. Phosphates, phosphites and thiophosphates of antimony compounds are cited. Oil-soluble antimony tris(O,O-dihydrocarbyl dithiophosphates) are indicated to be preferred.
U.S. Pat. No. 4,153,536 (1979) a divisional of U.S. Pat. No. 4,111,845 discloses the use of antimony and antimony-containing compounds to produce a cracking catalyst containing antimony in an amount sufficient to inhibit detrimental effects of metal contaminants such as nickel, vanadium and iron. Organic antimony compounds containing phosphorus atoms such as antimony phosphites, phosphates, thiophosphates and dithiophosphates are mentioned. However, the importance, if any, of the phosphorus alone as a passivating agent itself is neither suggested nor disclosed. The quantity of the antimony to be added to the cracking catalyst is the only feature of the antimony-containing compounds considered. The amount of phosphorus transferred to the cracking catalyst, if any, is not discussed.
U.S. Pat. No. 4,167,471 (1979) discloses a particular method for introducing a passivation stream, e.g., a fluid stream comprising hydrocarbons and an antimony-containing metals passivating agent, at a temperature below the decomposition temperature of such agent, into a cracking zone containing a cracking catalyst so as to maintain said agent substantially free of thermal decomposition until contacting said cracking catalyst. An example of such antimony-containing metals passivating agent cited was disclosed previously in U.S. Pat. No. 4,031,002 (1977) and contained phosphorodithioate ligands attached to antimony.
U.S. Pat. No. 4,169,784 (1979) discloses a method for the simultaneous use of a metals passivation agent and an oxidation promoter in a catalytic cracking system. Antimony compounds are indicated to be preferred for use as the metals passivation agent.
U.S. Pat. No. 4,169,042 (1979) discloses a treating agent for a hydrocarbon cracking catalyst. The adverse effects of nickel, vanadium and iron on cracking catalysts is either precluded or reduced by contacting the cracking catalyst with at least one treating agent selected from the group consisting of elemental tellurium, oxides of telurium and compounds convertible to elemental tellurium or oxides thereof during cracking or catalyst regeneration. The treating agent can be used either prior to, during or after a cracking catalyst is used in a hydrocarbon conversion process. The manner in which the conventional cracking catalyst is contacted with a modifying agent containing tellurium include solutions of water, hydrocarbon or aqueous acids contacting the cracking catalyst to result in an impregnation followed by volatilization of the liquid and precipitation of tellurium-containing compounds onto the catalyst from a treating solution.
Belgium Application 866,332, corresponding to U.S. application Ser. No. 819,027 (which issued as U.S. Pat. No. 4,141,858), discloses the use of antimony and/or bismuth-containing compounds to counteract the deactivating effect of metal contaminants such as nickel, iron and/or vanadium on clay-based cracking catalysts. Bismuth phosphate was expressly cited as an example of a bismuth-containing compound.
U.S. Pat. No. 4,183,803 (1980) discloses a process for the restoration of a used cracking catalyst, an improved catalytic cracking process which can provide a high yield and selectivity for gasoline and a modified cracking catalyst. The improved cracking catalyst involves restoring a used cracking catalyst contaminated by metals selected from the group consisting of nickel, vanadium and iron by contacting the use catalyst with antimony selenide, antimony sulfide, antimony sulfate, bismuth selenide, bismuth sulfide or bismuth phosphate.
The present invention is particularly suitable for passivating poisons in a catalyst utilized in the catalytic cracking of reduced or topped crude oils to more valuable products, such as illustrated in U.S. Pat. Nos. 3,092,568 and 3,164,542, the teachings of which are incorporated by reference herein. Similarly, this invention is applicable to processing shale oils, tar sands oils, coal oils and the like where metal contamination of the processing, e.g., cracking, catalyst can occur.